Download Of The Day: Trillian

Trillian by Cerulean Studios is a great download for anyone who loves chatting with friends and family online. This chat client supports programs like AIM, ICQ, MSN, Yahoo Messenger, and IRC and includes features like audio chat, file transfers, group chats, chat rooms, buddy icons, multiple simultaneous connections to the same network, server-side contact importing, typing notification, direct connection (AIM), proxy support, encrypted messaging (AIM/ICQ), SMS support, and privacy settings.
Click here to download Trillian and see a feature tour of this all-in-one chat program which boasts many more superior features.

I've been using it for about 4 years now.
It hasn't been updated in over 2 years. It's kind of quirky and takes a while to get used to. There are better options out there now, I think.
Check out meebo.com and GAIM